What causes your stool to be green? Had lunch at arby's today and since I have used the restroom a couple of times it's comes out green.

Fat in food. High fatty processed foods cause increase in bile from the gallbladder. This reaction may be evidence that you and arby's don't mix well.
Green . Green stool is not a worry, probably just from the foods you have been eating like spinach. Bile is greenish too, and so that can colour the stool as well.